Longitudinal field driven ion mobility filter and detection system

ABSTRACT

An asymmetric field ion mobility spectrometer for filtering ions via an asyretric electric field, an ion flow generator propulsing ions to the filter via a propulsion field.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.10/082,803, filed Feb. 21, 2002, which is a Continuation-In-Part of U.S.application Ser. No. 09/439,543, filed Nov. 12, 1999, which is aContinuation-In-Part of U.S. application Ser. No. 09/358,312, filed Jul.21, 1999, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to chemical analytical systems based onion mobility, and conveyance of ions through such a system.

BACKGROUND OF THE INVENTION

The ability to detect and identify explosives, drugs, chemical andbiological agents as well as monitor air quality has become increasinglymore critical given increasing terrorist and military activities andenvironmental concerns. Previous detection of such agents wasaccomplished with conventional mass spectrometers, time of flight ionmobility spectrometers and conventional field asymmetric ion mobilityspectrometers (FAIMS).

Mass spectrometers are very sensitive and selective with fast responsetime. Mass spectrometers, however, are large and require significantamounts of power to operate. They also require a powerful vacuum pump tomaintain a high vacuum in order to reduce ion neutral interactions andpermit detection of the selected ions. Mass spectrometers are also veryexpensive.

Another spectrometric technique which is less complex is time of flightion mobility spectrometry which is the method currently implemented inmost portable chemical weapons and explosives detectors. The detectionis based not solely on mass, but on charge and cross-section of themolecule as well. However, because of these different characteristics,molecular species identification is not as conclusive and accurate asthe mass spectrometer. Time of flight ion mobility spectrometerstypically have unacceptable resolution and sensitivity limitations whenattempting to reduce their size. In time of flight ion mobility, theresolution is proportional to the length of the drift tube. The longerthe tube the better the resolution, provided the drift tube is also wideenough to prevent all ions from being lost to the side walls due todiffusion. Thus, fundamentally, miniaturization of time of flight ionmobility systems leads to a degradation in system performance. Whileconventional time of flight devices are relatively inexpensive andreliable, they suffer from several limitations. First, the sample volumethrough the detector is small, so to increase spectrometer sensitivityeither the detector electronics must have extremely high sensitivity,requiring expensive electronics, or a concentrator is required, addingto system complexity. In addition, a gate and gating electronics areusually needed to control the injection of ions into the drift tube.

FAIMS spectrometry was developed in the former Soviet Union in the1980's. FAIMS spectrometry allows a selected ion to pass through afilter while blocking the passage of undesirable ions. But the onlycommercial prior art FAIMS spectrometer was large and expensive, e.g.,the entire device was nearly a cubic foot in size and cost over $25,000.Such systems are not suitable for use in applications requiring smalldetectors. They are also relatively slow, taking as much as one minuteto produce a complete spectrum of the sample gas, are difficult tomanufacture and are not mass producible.

The prior art FAIMS devices depend upon a carrier gas that flows in thesame direction as the ion travel through the filter. However, the pumpsrequired to draw the sample medium into the spectrometer and to providea carrier gas can be rather large and can consume large amounts ofpower.

It is therefore an object of the present invention to provide an ionfilter and detection system which does not require the high flow rate,high power consumption pumps normally associated with FAIMSspectrometers.

It is another object of the present invention to provide method andapparatus for highly efficient conveyance of ions into and through ahigh field ion mobility filter.

It is a further object of the present invention to provide method andapparatus for efficient conveyance of ions into and through a high fieldion mobility filter without the use of a carrier gas.

It is another object of the present invention to provide a FAIMS filterand detection system which can quickly and accurately control the flowof selected ions to produce a sample spectrum.

It is a further object of the present invention to provide a FAIMSfilter and detection system which has a sensitivity of parts per billionto parts per trillion.

It is a further object of the present invention to provide a FAIMSfilter and detection system which may be packaged in a single chip.

It is a further object of the present invention to provide a FAIMSfilter and detection system which is cost effective to implement,produce and operate.

SUMMARY OF THE INVENTION

The present invention features an ion mobility spectrometer forfiltering ions via an asymmetric electric field. Ions are transportedalong the longitudinal ion flow path via an ion flow generator. The ionflow generator preferably provides ion propulsion via a local electricfield in the flow path. Operation of the invention enables eliminationor reduction of flow rate and power requirements of conventional gasflow.

In a preferred embodiment, a longitudinal electric field generated bythe ion flow generator propels ionized sample received from anionization region through a compensated, asymmetric electric field ofthe ion filter, with a desired species passing through the filter andflowing toward a detector region. Various options are possible. In oneembodiment, a low volume gas flow carries the sample to the filter. Inother embodiment, there is no need for gas flow and ion steering, or thelongitudinal field itself, propels ions into the filter region, wherethe ions are further propelled by the ion flow generator.

In another embodiment, a supply of clean filtered air is flowed in thenegative longitudinal direction opposite the desired direction of ionflow to keep the ion filter and detector regions free of neutrals and tohelp remove solvent, reduce clustering, and minimize the effects ofhumidity.

A preferred embodiment of the present invention features an ion mobilityspectrometer having a housing structure that defines a flow path (alsoknown as a drift tube) that begins at a sample inlet for receipt ofsample (i.e., sample molecules to be analyzed) and brings the sample toan ionization region. Once ionized, the sample passes to the ion filter,with desired ion species passing through the filter in the flow path, aspropelled by the ion flow generator.

In one embodiment, the ion filter is provided with a plurality of highfrequency, high voltage filter electrodes for creation of the asymmetricelectric field transverse to the longitudinal ion flow direction alongthe flow path. In a preferred embodiment, this field is compensated, topass only a desired ion species for downstream detection. In anotherembodiment, filtering is trajectory based without requiringcompensation.

The ion flow generator creates a longitudinal electric field along theflow path (transverse to the asymmetric electric field) for propellingor transporting the ions through the asymmetric electric field towardthe output region to enable detection and analysis. The ionizationsource may include a radiation source, an ultraviolet lamp, a coronadischarge device, electrospray nozzle, plasma source, or the like.

In one embodiment, an electric controller supplies a compensation biasand an asymmetric periodic voltage to the ion filter. The ion filtertypically includes a pair of spaced electrodes for creating theasymmetric electric field between the electrodes. The ion flow generatortypically includes a plurality of spaced discrete electrodes proximateto the filter electrodes for creating a longitudinal direction electricfield which propels the ions through the transverse asymmetric electricfield, and onward for detection. The ion filter and flow generator mayshare none, some or all electrodes.

In another embodiment, the ion flow generator includes spaced resistivelayers and a voltage is applied along each layer to create thelongitudinally directed electric field which propels the ions throughthe filter's compensated asymmetric electric field and to the detector.

In another embodiment, the ion filter includes a first plurality ofdiscrete electrodes electrically connected to an electric controllerwhich applies the asymmetric periodic voltage to them. The ion flowgenerator includes a second plurality of discrete electrodes dispersedamong the electrodes of the ion filter and connected to a voltage sourcewhich applies a potential gradient along the second plurality ofdiscrete electrodes. Compensation voltage applied to the filter opensthe filter to pass a desired ion species if present in the sample. Ifthe compensation voltage is scanned, then a complete spectrum of thecompounds in a sample can be gathered.

In one embodiment, the ion filter includes electrodes on an insidesurface of the housing and the ion flow generator includes electrodesproximate to the ion filter electrodes. The housing may be formed usingplanar substrates. The ion detector also includes electrodes on aninside surface of the housing proximate to the ion filter and the ionflow generator.

In another embodiment, the ion filter may include electrodes on anoutside surface of the housing and the ion flow generator then includesresistive layers on an inside surface of the housing. A voltage isapplied along each resistive layer to create a longitudinal electricfield. Alternatively, the ion filter and the ion flow generator arecombined and include a series of discrete conductive elements eachexcited by a voltage source at a different phase.

In another embodiment, both the longitudinal and transverse fields andvoltages are applied or generated via the same electrodes or via membersof a set of electrodes. Because of the flexibility of the electronicdrive system of the invention, all or part of the electrode set may beused for a given function or more than one function in series orsimultaneously.

In yet a further embodiment of the invention, filtering is achievedwithout compensation of the filter field. In one practice, thespectrometer has a single RF (high frequency, high voltage) filterelectrode on a first substrate, and a plurality of multi-functionelectrodes on a second substrate that are formed facing the filterelectrode over the flow path. The plurality of electrodes forms asegmented detector electrode. Ions are filtered and detected bytrajectory, being controlled by the asymmetric field and landing on anappropriate one of the detector electrode segments. Thus filtering isachieved without compensation of the filter field in a very compactpackage. The detector electrodes are monitored, wherein a particularspecies can be identified based on its trajectory for a given detectionand given knowledge of the signals applied, the fields generated, andthe transport (whether gas or electric field).

In practice of the invention, prior art pumps used to draw a sample,such as a gas containing compounds to be analyzed, into a FAIMSspectrometer, and to provide a flow of carrier gas, can be made smalleror even eliminated in practice of the invention. This is enabled inpractice of the invention by incorporation of an ion flow generatorwhich creates a longitudinal electric field in the direction of theintended ion travel path to propel the ions toward a detector regionafter passing through a transversely directed asymmetric electric fieldwhich acts as an ion filter.

The result is the ability to incorporate lower cost, lower flow rate,and smaller, even micromachined pumps, in embodiments of the invention;a decrease in power usage; the ability to apply clean filtered gas(e.g., dehumidified air) in a direction opposite the direction of iontravel to eliminate ion clustering and the sensitivity of thespectrometer to humidity. Separate flow paths for the source gas and theclean filtered gas may not be required, thus reducing the structure usedto maintain separate flow paths taught by the prior art. Moreover, if anelectrospray nozzle is used as the ionization source, the electrodesused to create the fine droplets of solvent can be eliminated becausethe electrodes which create the longitudinal and transverse electricfields can be used to function both to transport the ions and to createthe fine spray of solvent droplets.

In a practice of the invention, an extremely small, accurate and fastFAIMS filter and detection system can be achieved by defining anenclosed flow path between a sample inlet and an outlet using a pair ofspaced substrates and disposing an ion filter within the flow path, thefilter including a pair of spaced electrodes, one electrode associatedwith each substrate and a controller for selectively applying a biasvoltage and an asymmetric periodic voltage across the electrodes tocontrol the path of ions through the filter. In a further embodiment ofthe invention, it is possible to provide an array of filters to detectmultiple selected ion species.

Alternative filter field compensation in practice of embodiments of theinvention may be achieved by varying the duty cycle of the periodicvoltage, with or without a bias voltage. Furthermore, in an embodimentof the invention, it is possible that by segmenting the detector, iondetection may be achieved with greater accuracy and resolution bydetecting ions spatially according to the ions' trajectories as the ionsexit the filter.

It will be further understood that while ion travel within the ionfilter is determined by the compensated asymmetric filter field and theion transport field, the invention may also include an ion concentratingfeature for urging ions toward the center of the flow path. In oneembodiment this concentrating is achieved where fields betweenelectrodes on each substrate work together to urge the ions toward thecenter of the flow path as they pass there between approaching the ionfilter.

In other embodiments, ion filtering is achieved without the need forcompensation of the filter field. In one illustrative embodiment, aspectrometer of the invention has preferably a single RF (highfrequency, high voltage) filter electrode. A segmented filter-detectorelectrode set faces the first electrode over the flow path, with thefilter-detector electrode set having a plurality of electrodes in a rowmaintained at virtual ground. The asymmetric field signal is applied tothe filter electrode and the asymmetric field is generated between thefilter electrode and the filter-detector electrode set. Ions flow in thealternating asymmetric electric field and travel in oscillating pathsthat are vectored toward collision with a filter electrode, and inabsence of compensation, favorably enables driving of the ions tovarious electrodes of the filter-detector electrode set. Thesecollisions are monitored.

In a further embodiment, upstream biasing effects which ions flow to thefilter. For example, a sample flows into an ionization region subject toionization source, and electrodes are biased to deflect and affect flowof the resulting ions. Positive bias on a deflection electrode repelspositive ions toward the filter and attracting electrodes beingnegatively biased attract the positive ions into the central flow of theion filter, while negative ions are neutralized on the deflectionelectrode and which are then swept out of the device. Negative bias onthe deflection electrode repels negative ions toward the filter andattracting electrodes positively biased attract the negative ions intothe central flow path of the filter, while positive ions are neutralizedon the deflection electrode.

In an embodiment, the path taken by a particular ion in the filter ismostly a function of ion size, cross-section and charge, which willdetermine which of the electrodes of the filter-detector electrode setthat a particular ion species will drive into. This speciesidentification also reflects the polarity of the ions and the high/lowfield mobility differences (“alpha”) of those ions. Thus a particularion species can be identified based on its trajectory (i.e., whichelectrode is hit) and knowledge of the signals applied, the fieldsgenerated, and the transport characteristics (such as whether gas orelectric field).

In practice of the filter function of the invention, where the upstreambiasing admits positive ions into the filter, those positive ions withan alpha less than zero will have a mobility decrease with an increaseof a positively offset applied RF field. This will affect the trajectoryof these ions toward the downstream detector electrodes. However, apositive ion with an alpha greater than zero will have a mobilityincrease with an increase of a negatively offset applied RF field, whichin turn will shorten the ion trajectory toward the nearer detectorelectrodes.

Similarly, where the filter received negative ions, a negative ion withan alpha less than zero will have a mobility increase with an increaseof a positively offset applied RF field; this will tend to affect theion trajectory toward the downstream detector electrodes. However, anegative ion with an alpha greater than zero will have a mobilityincrease with an increase of a negatively offset applied RF field, whichin turn will tend to shorten the ion trajectory toward the nearerdetector electrodes. Thus, ions can be both filtered and detected in aspectrometer of the invention without the need for compensation.

In various embodiments of the invention, a spectrometer is providedwhere a plurality of electrodes are used to create a filter field and apropulsion field, in a cooperative manner that may be featuresimultaneous, iterative or interactive use of electrodes. Where aplurality of electrodes face each other over a flow path, the filterfield and the propulsion field may be generated using the same ordifferent members of the electrode plurality. This may be achieved in asimple and compact package.

In practice of the invention, a spectrometer is provided in variousgeometries where a plurality of electrodes are used to create a filterand a propulsion field, in a cooperative manner that may be simultaneousor interactive. Where a plurality of electrodes face each other over aflow path, the filter field and the propulsion field may be generatedusing the same or different members of the electrode plurality to passselected ion species through the filter.

It will be appreciated that in various of the above embodiments, aspectrometer can be provided in any arbitrarily shaped geometry (planar,coaxial, concentric, cylindrical) wherein one or more sets of electrodesare used to create a filtering electric field for ion discrimination.The same or a second set of electrodes, which may include an insulativeor resistive layer, are used to create an electric field at some angleto the filtering electric field for the purpose of propelling ionsthrough the filtering field to augment or replace the need forpump-driven propulsion such as with a carrier gas.

It will now be appreciated that a compact FAIMS spectrometer has beenprovided with e-field ion propulsion. Benefits of the invention includeprovision of a stable, easily controlled ion flow rate without the needfor gas flow regulation. Elimination of the need for gas flow regulationreduces complexity and cost and improves reliability. Dramatic reductionof gas flow substantially reduces power consumption. Operation of theinvention can reduce the amount of sample neutrals entering the analysisregion between the filter electrodes. If only ions are injected into thefilter, then it is easier to keep the ion filter in a controlledoperating state, such as control of moisture level. The result is veryreproducible spectra in a low power analytical system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic block diagram of a PFAIMS filter and detectionsystem according to the present invention.

FIG. 2 is a schematic representation of the ions as they pass throughthe filter electrodes of FIG. 1 toward the detector.

FIGS. 3A, 3B provide graphical representation of an asymmetric periodicvoltage having a compensating varying duty cycle, for filtering unwantedions (FIG. 3A) and passing through the filter selected ion species (FIG.3B) without a bias voltage.

FIG. 4 is a schematic diagram of a segmented detector embodiment of theinvention.

FIGS. 5A, 5B are graphical representations of the spectrometer responseto varying concentrations of acetone and di-ethylmethyl amine in anembodiment of the invention.

FIG. 6 is a cross sectional view of a spaced, micromachined filterassembly according to an embodiment of the present invention.

FIG. 7 is a perspective view of a practice of the invention as apackaged micromachined filter and detection system, including pumps, inminiaturized format.

FIG. 8 is a cross sectional view of a dual channel embodiment of theinvention.

FIG. 9 is a schematic view of a prior art spectrometer.

FIGS. 10-17 are respective schematic views of embodiments of thelongitudinal field driven ion mobility spectrometer of the presentinvention.

FIG. 18 is an embodiment of the invention that performs ion filteringbased on ion trajectory within the filter region.

FIG. 19 is a graphical representation of identification of chemicalconstituents of a mixture (benzene and acetone) in practice of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A description of preferred embodiments of the invention follows.

A preferred embodiment of the present invention provides method andapparatus for conveyance of ions in and through an ion filter withoutthe need for a carrier gas in an ion-mobility-based analytical system.In embodiments of the present invention, the need for pumps is eithereliminated or the pumps are made smaller, even micromachined.Furthermore, separate flow paths for the source gas and the carrier gasare not required. In one filter embodiment, filtered gas is introducedto flow in a direction opposite the direction of ion travel to eliminateion clustering and to improve system sensitivity. Preferred andalternative embodiments of the invention are set forth below as anillustration and as a limitation.

A preferred planar FAIMS (PFAIMS) spectrometer 10, FIG. 1, operates bydrawing a carrier gas 12 containing a sample S to be analyzed (oftencollectively referred to as a gas sample), by means of pump 14, throughinlet 16 and into ionization region 17. The gas sample is ionized byionization source 18. Source 18 may include an ultraviolet light source,a radioactive device, plasma source, corona discharge device,electrospray head, or the like.

The ions 19 flow from the ionization region 17 along flow path 26 intofilter 24 defined by facing electrodes 20 and 22. As these ions passbetween electrodes 20 and 22 they are exposed to an asymmetric electricfield 25 established between the filter electrodes, induced by a voltageapplied from a source, such as voltage generator 28 directed byelectronic controller 30. Filter field 25 is transverse to thelongitudinal flow of gas and ions along flow path 26.

The system is preferably driven by electronic controller 30, which mayinclude, for example, amplifier 34 and microprocessor 36. Amplifier 34amplifies the output of detector 32, which is a function of the chargecollected by electrode 35 and provides the output to microprocessor 36for analysis. Similarly, amplifier 34, shown in phantom, may be providedwhere electrode 33 is also utilized as a detector.

As part of the FAIMS filtering function, some compensation must beapplied to the filter; which in turn selects a particular ion speciesthat will pass through the filter. In operation, as ions pass throughfilter field 25, some ions are neutralized as they travel into andcollide with filter electrodes 20 and 22. However the filter field iscompensated to bring a particular species of ion back toward the centerof the flow path, preventing it from being neutralized. Thus a desiredion species 19′ passes through the filter.

More specifically, as shown in FIG. 2, ions 19 flow in the alternatingasymmetric electric field 25, in oscillating paths 42 a, 42 b and 42 c.The time varying RF asymmetric voltage V applied to the filterelectrodes is typically in the range of ±(1000-10,000) volts and createselectric field 25 with a maximum field strength of around 40,000 V/cm.The path taken by a particular ion is mostly a function of its size,cross-section and charge. Where the asymmetric field is not compensatedfor the resulting high-low-field offset imposed on the ions, then theions will reach and contact electrode 20 or 22 and will be neutralized.Thus as compensation is applied to the filter field, a particular ionspecies will be returned back toward the center of the flow path andwill pass through the filter for detection.

In a particular embodiment, compensation is achieved by applying acompensation field 44, typically in the range of ±2000 V/cm from anapplied ±100 volt dc voltage, for example, applied concurrently andinduced at, adjacent to, or between, electrodes 20 and 22, via a biasvoltage applied thereto. Now a selected ion species 19′ passes throughfilter 24 for detection.

In one embodiment, compensation field 44 is a constant bias whichoffsets alternating asymmetric field 25 to allow the selected ionspecies 19′ to pass to detector 32. Thus, with the proper bias voltage,a particular species of ion will follow path 42 c while undesirable ionswill follow paths 42 a and 42 b to be neutralized as they encounterelectrode plates 20 and 22.

In an alternative practice of the invention, the duty cycle of theasymmetric periodic voltage applied to electrodes 20 and 22 of filter 24is varied so that there is no need to apply a compensation voltage. Thecontrol electronics varies the duty cycle of asymmetric alternatingelectric field 25, with the result that path of a selected ion species(defined mostly by charge and cross-section, among othercharacteristics, of the ions) is returned toward the center of the flowpath, and so to pass on for detection. As an example, and not by way oflimitation, the duty cycle of field 25 may be one quarter: 25% high,peak 70, and 75% low, valley 72; in which case, ions 19 on path 42 aapproach and collide with a filter electrode 20 and are neutralized(FIG. 3A). However, by varying the duty cycle to 40%, peak 70 a, 60%low, valley 72 a, ions 19′ on path 42 c pass through filter 24 andtoward the detector without being neutralized. Typically the duty cycleis variable from 10-50% high and 90-50% low (FIG. 3B). Accordingly, byvarying the duty cycle of field 25 an ion's path in field 25 may becorrected so that it will pass through filter 24 without beingneutralized and without the need for a compensating bias voltage.

Ions 19′ that pass through filter 24 are now delivered for detection,which may be on-board or not. In a preferred embodiment, the detector ison board and is in the flow path. In one embodiment, detector 32includes a biased top electrode 33 at a voltage and a biased bottomelectrode 35, possibly at ground, formed on the same substrates as thefilter electrodes. Top electrode 33 can be set at the same polarity asthe ions to be detected and therefore deflects ions toward electrode 35.However, either electrode may detect ions depending on the passed ionspecies and bias applied to the electrodes. Moreover, multiple ions maybe detected by using top electrode 33 as one detector and bottomelectrode 35 as a second detector.

The output of FAIMS spectrometer 10 is a measure of the amount of chargedetected at detector 32 for a given RF field 25 and compensation. Thelonger the filter 24 is set at a given compensation level, the more of agiven species will be passed and the more charge will accumulate ondetector 32.

Alternatively, by sweeping compensation over a predetermined voltagerange, a complete spectrum for the sample and gas can be achieved. AFAIMS spectrometer according to the present invention requires typicallyless than thirty seconds and as little as one second or less to producea complete spectrum for a given gas sample. Thus, by varyingcompensation during a scan, a complete spectrum of the gas sample can begenerated.

To improve FAIMS spectrometry resolution even further, detector 32, maybe segmented, as shown in FIG. 4. As ions pass through filter 24 betweenfilter electrodes 20 and 22, the individual ions 19-19 may be detectedspatially, the ions having their trajectories 42 c-42 c determinedaccording to their size, charge and cross section. Thus detector segment33′ will have a concentration of one species of ion while detectorsegment 33 will have a different ion species concentration, increasingthe spectrum resolution as each segment may detect a particular ionspecies.

A PFAIMS spectrometer as set forth herein is able to detect anddiscriminate between a wide range of compounds, and can do so with highresolution and sensitivity. As shown in FIG. 5A, varying concentrationsof acetone that were clearly detected in one practice of the invention,with definitive data peaks 46 at −3.5 volts compensation. These weredetected even at low concentrations of 83 parts per billion. With thebias voltage set at −6.5 volts, FIG. 5B, varying concentrations ofdiethyl methyl amine were clearly detected in practice of the invention,generating data peaks 46; these were detected in concentrations as lowas 280 parts per billion.

Turning to FIG. 6 and FIG. 7, an embodiment of spectrometer 10 includesspaced substrates 52 and 54, for example glass or ceramic, andelectrodes 20 and 22, which may be for example gold, titanium, orplatinum, mounted or formed on substrates 52 and 54, respectively.Substrates 52 and 54 are separated by spacers 56 a-b which may be formedby etching or dicing silicon wafer. The thickness of spacers 56 a, 56 bdefines the distance between electrodes 20 and 22.

In one embodiment, a voltage is applied to silicon spacers 56 a-b,±(10-1000 volts dc), which transforms spacers 56 a and 56 b intoelectrodes to produce a confining electric field 58. Field 58 guides orconfines the ions' paths to the center of flow path 26 in order toobtain more complete sample collection. As will be understood by aperson skilled in the art, spacer electrodes 56 a-b must be set to theappropriate voltage so as to “push” the ions toward the center of flowpath 26. More ions traveling in the center of the path makes possiblethe result of more ions striking electrodes 33 and 35 for detection.However, this is not a necessary limitation of the invention.

Embodiments of the invention are compact with low parts count, where thesubstrates and spacers act to both contain the flow path and also to fora structural housing of the invention. Thus the substrates and spacersserve multiple functions, both for guiding the ions and for containingthe flow path.

In order to further assure accurate and reliable operation ofspectrometer 10, neutralized ions which accumulate on electrode plates20 and 22 are purged. In one embodiment this may be accomplished byheating flow path 26. For example, controller 30, FIG. 1, may includecurrent source 29, shown in phantom in FIG. 6, which provides, inresponse to microprocessor 36, a current I to electrode plates 20 and 22to heat the electrodes for removing accumulated neutrals. Optionally,current I may additionally or instead be applied to spacer electrodes 56a and 56 b, to heat flow path 26 to purge electrodes 20 and 22.

A packaged FAIMS spectrometer 10 may be reduced in size to perhaps oneinch by one inch by one inch. Pump 14 is mounted on substrate 52 fordrawing gas sample 12 into inlet 16. Clean dry air may be introducedinto flow path 26 by recirculation pump 14 a prior to or afterionization of the gas sample. Electronic controller 30 may be etchedinto silicon control layer 60 which combines with substrates 52 and 54to form a housing for spectrometer 10. Substrates 52 and 54 and controllayer 60 may be bonded together, for example, using anodic bonding, toprovide an extremely small FAIMS spectrometer. Micro pumps 14 and 14 aprovide a high volume throughput which further expedites the analysis ofgas sample 12. Pumps 14 and 14 a may be, for example, conventionalminiature disk drive motors fitted with small centrifugal air compressorrotors or micromachined pumps, which produce flow rates of 1 to 4 litersper minute.

In practice of ion detection, generally speaking, sample ions tend to befound in either monomer or cluster states. It has been found that therelationship between the amount of monomer and cluster ions for a givenion species is dependent of the concentration of sample and theparticular experimental conditions (e.g., moisture, temperature, flowrate, intensity of RF-electric field). Both the monomer and clusterstates provide useful information for chemical identification. It willbe useful to investigate the same sample separately in a condition whichpromotes clustering and in an environment that promotes the formation ofonly the monomer ions. A two channel PFAIMS of an embodiment such asshown in FIG. 8 can be used toward this end.

Dual chamber embodiment 10 x of the invention, FIG. 8, has two enclosedflow paths 26′, 26″ coupled by passageway 63. The gas sample 12 entersinlet 16 a and is ionized at ionization region 17 in the lower flow path26′, ionized by any ionization device, such as an internal plasma source18 a. The ions are guided toward ion filter 24 a in upper flow path 26″through passageway 63 by electrodes 56 ax and 56 bx, which act assteering or deflecting electrodes, and may be defined by confiningelectrodes 56 a, 56 b. As these ions 42 c pass between ion filterelectrodes 20 a and 22 a, undesirable ions will be neutralized byhitting the filter electrodes while selected ions will pass throughfilter 24 a to be detected by detector 32 a, according to the applied RFand compensation. By deflecting ions out of the gas flow, a preliminaryfiltration is effected, wherein the non-deflected ions and non-ionizedsample and associated carrier gas will be exhausted at outlet 16 x′. Theexhaust gas 43 from upper flow path 26″, at outlet 16 x″, may becleaned, filtered and pumped via pump part 14 a and returned at inlet 16b as clean filtered gas 66 back into the flow path 26″.

In one practice of the invention, clean dry air 66 a may be introducedinto flow path 26 through clean air inlet 66 via pump 14. Drawing inclean dry air assists in reducing the FAIMS spectrometer's sensitivityto humidity. Moreover, if the spectrometer is operated alternately withand without clean dry air, and with a known gas sample introduced intothe device, then the device can be used as a humidity sensor since theresulting spectrum will change with moisture concentration from thestandardized spectrum for the given known sample.

In operation of the embodiment of FIG. 8, independent control of theflow rates in flow paths 26′, 26″ may be made. This means that a higheror lower flow rate in flow path 26′ of the sample can be used, dependingon the particular front end environment system, while the flow rate ofthe ions through the ion filter in flow path 26″ can be maintainedconstant, allowing, consistent, reproducible results.

In practice of this embodiment, the upper ion filter region in flow path26″ can be kept free of neutrals. This is important when measuringsamples at high concentrations, such as those eluting from a GC column.Because the amount of ions the ionization source can provide is fixed,if there are too many sample molecules, some of the neutral samplemolecules may cluster with the sample ions and create large moleculeswhich do not look at all like the individual sample molecules. Byinjecting the ions into the clean gas flow in flow path 26″, and due tothe effect of the high voltage high frequency field, the molecules willde-cluster, and the ions will produce the expected spectra.

Another advantage of the embodiment of FIG. 8 is that the dynamic rangeof the PFAIMS detector can be extended when employing a front end device(such as a GC, LC or electrospray for example). In one practice of theinvention, by adjusting the ratios of the drift gas andGC-sample/carrier gas volume flow rates coming into ionization region17, the concentration of the compounds eluting from the GC can becontrolled/diluted in a known manner so that samples are delivered tothe PFAIMS ion filter 24 at concentrations which are optimized for thePFAIMS filter and detector to handle. In addition, steering electrodes56 ax, 56 bx can be pulsed or otherwise controlled to determine how manyions at a given time enter into flow path 26″.

In a further practice of the embodiment of FIG. 8, an additional PFAIMSfilter 24 b may be provided in lower flow path 26′ for detection of ionspecies that have not been deflected into flow path 26″ and thus thatpass into filter 24 b. Filter 24 b includes electrodes 20 b, 22 b, shownin phantom, and possibly also detector 32 b having electrodes 33 b, 35b, in phantom.

In the embodiment of FIG. 8, different gas conditions may be presentedin each flow path. With a suitable control applied to the two steeringelectrodes 56 ax, 56 bx, selection can be made as to which region theions are sent. Because each chamber can have its own gas and biascondition, multiple sets of data can be generated for a single samplesimultaneously. This enables improved species discrimination in a simplestructure, regardless of whether or not a front end device (such as aGC) is used for sample introduction.

One prior art ion mobility spectrometer 200, FIG. 9, (See U.S. Pat. No.5,420,424), includes analytical gap 202 defined by the space betweeninner cylindrical filter electrode 204 and outer cylindrical filterelectrode 206 electrodes. A source gas having compounds to be analyzedis drawn through inlet 210 via the action of pump 212; the sample isionized by ionization source 214. A carrier gas CG is introduced viapump 216 into analytical gap 202. Ions generated by ionization source214 travel through aperture 218 by the action of electrode 220 and intoanalytical gap 202 and travel toward detector 224. Such a structurerequires two pumps 212 and 216, and separate flow paths 201 and 203 forthe source gas and the carrier gas. Thus, prior art mobilityspectrometer 200 cannot be made very small, and requires sufficientpower to operate the pumps 212 and 216.

Embodiments of the present invention overcome limitations of the priorart by providing field-driven ion transport via an ion flow generator,where ions flow through an ion filter as carried by the ion transportfield. The ion flow generator of the present invention relieves the gasflow requirements of the prior art. Various options are possible,including providing a low volume flow, no gas flow, or reverse gas flow,along the longitudinal axis of the flow path. The reverse flow can be asupply of clean filtered air in the negative z direction to keep the ionfilter and detector regions free of neutrals and to help remove solvent,reduce clustering, and minimize the effects of humidity. The ion flowgenerator is preferably based on electric potentials, but may bepracticed in magnetic embodiments, among others, and still remain withinthe spirit and scope of the present invention. Various embodimentsfollow by way of illustration and not by way of limitation.

In one practice of the invention, shown in FIG. 10, field asymmetric ionmobility spectrometer 230 includes a flow path 231 inside housingstructure 234 (which may be formed by a round tube or a flat housingwith walls defining an enclosure). A source gas carries sample S intothe ionization region near the ionization source 236. This flow issupplied by pump 238, which may be a micromachined pump with a flow rateof much less than the typically required 1-4 liters per minute of theprior art (resulting in a power savings of between 1-5 watts over priorart spectrometers). Alternatively, this flow might be supplied by sampleeluting from a GC column or the like.

Ion filter 240 is disposed in flow path 231 downstream from ionizationsource 236. Ion filter 240 creates the asymmetric electric field 242 (acompensated field 25), to filter ions generated by ionization of sampleS. Ion filter 240 may include a pair of spaced electrodes 248 and 246connected to an electric controller which applies a compensatedasymmetric periodic voltage to electrodes 246 and 248.

In spectrometer 230, ion flow generator 250 provides longitudinalelectric field transport for the ions. The strength of longitudinalelectric field 252 can be constant or varying in time or space; thefield propels ions through the filter asymmetric field 242, with ionspassing through the filter according to their characteristics and thefilter field compensation.

In the embodiment of FIG. 10, ion flow generator 250 includes discreteelectrodes 260, 262, 264, and 266 supported by and insulated from filterelectrode 246 by insulating medium 268, and discrete electrodes 261,263, 265, and 267 supported by and insulated from filter electrode 248by insulating medium 269. In one practice of the invention, electrodes260, 261 are at 1,000 volts and electrodes 266, 267 are at 10 volts andelectrode pairs 262, 263 and 264, 265 are at 500 and 100 volts,respectively, although these voltage levels vary or be varying dependingon the specific implementation of spectrometer 230. There may be more orfewer electrodes opposing each other forming ion flow generator 250.Electrode pairs (260, 261), (262, 263), (264, 265), and (266, 267) canalso each be a ring electrode as well as discrete planar electrodes. Thestrength of longitudinal electric field 252 propels ions generated ationization source 236 through asymmetric electric field 242 and towarddetector 270, thus eliminating or reducing the flow rate and powerrequirements of pumps 212 and 216, FIG. 9 of the prior art.

Typically, detector 270 (which may have the configuration shown earlierof two electrodes 33, 35 on substrates 52, 54) is positioned close toion flow generator 250. Electrodes 260, 262, 264, 266, 261, 263, 265,and 267 preferably occupy more or less the same longitudinal space asion filter 240 and its electrodes 246 and 248 relative to a gap 232 inflow path 231.

In the embodiment of the invention shown in FIG. 11, ion filter 240includes spaced electrodes 276 and 277 for creating transverse filterfield 242. The ion flow generator 250 includes spaced discreteelectrodes, such as electrode pairs 282-284 and 286-288, for generatinglongitudinal transport field 252. In one practice, electrodes 282 and284 are at 1000 volts and electrodes 286 and 288 are at 1000 volts.Insulating medium 290 and 291 insulates electrodes 282, 284, 286, and288 with respect to electrodes 276 and 277. Electrode pair 282-284 couldalso be coupled as a single ring electrode and electrode pair 286-288could be coupled also be a single ring electrode in a cylindricalembodiment of the invention.

It will be appreciated that the sample must be conveyed to theionization region and the ions must be conveyed into the filter. In thedesign of FIG. 11, the ions are propelled by a low volume flow along thedirection of the longitudinal electric field 252 to bring the ionsproximate to electrodes 282-284. No gas flow is required in the ionfilter and detector region due to longitudinal electric field 252. Alsoin this embodiment, a low flow volume of clean filtered air optionallycan be provided in a direction opposite the longitudinal electric fieldto keep the ion filter and detector region free of neutrals. A resistivedivider circuit or the like can be used to provide a potential gradient,so that for example, electrodes 282 and 284 are at 1000 volts whileelectrodes 286 and 288 are at 0 volts.

An alternative practice of the invention is shown in FIG. 12, havingmetal filter electrodes 276, 277 deposited on insulating substrates 310,311 and filter electrodes 276, 277 coated with a thin insulator 290,291. Metal electrodes, e.g., 312, 314, 316, 318, are formed under aresistive layer 300, 302, and the longitudinal field is generatedbetween these electrodes. In one practice, ion filter 240 includesspaced resistive layers 300 and 302 insulated from electrodes 276 and277 on insulating substrates 310, 311 by insulating medium 290 and 291,for example, a low temperature oxide material. Resistive layers 300 and302 may be a resistive ceramic material deposited on insulating layers290 and 291, respectively. Terminal electrodes 312, 314, 316 and 318make contact with each resistive layer to enable a voltage drop acrosseach resistive layer that generates the longitudinal electric field 252,for example, where electrodes 312 and 316 are at 1000 volts whileelectrodes 314 and 318 are at 0 volts. This embodiment can be extendedto a cylindrical geometry by making electrodes 312 and 316 a ringelectrode, electrodes 314 and 318 a ring electrode, and resistive layers300 and 302 an open cylinder.

Continuing with the benefits of a dual flow path, such as earlier shownin FIG. 8, in the embodiment of FIG. 13 spectrometer 320 includesstructure which also defines dual flow paths 321, 323. Ion filter 240and ion flow generator 250 are defined by sets of electrodes in thisembodiment. Gap 304 is defined in flow path 323 at filter 240. Opening306 joins the flow paths. Source gas carrying sample S to be analyzed isdrawn into flow path 302 by pump 310 and ionized by ionization source308. The ions are deflected through opening 306 and into gap 304assisted by deflecting electrodes 312 and 313. Ion flow generator 250propels the ions through the asymmetric ion field at filter 240.Optionally pump 312 can be used to supply a low flow rate of air,possibly dehumidified, into, or recirculating through, gap 304, but nocarrier gas flow is required in flow path 302. Ion species passed by thefilter are carried by the ion transport 252 to detector 270.

In another embodiment of the invention, shown in FIG. 14, spectrometer325 includes a desiccant 322 chambered in housing 326 and small pump324, which is the only pump required to draw source gas into housing 326through a small orifice 327. Ionization source 328 produces ions whichtravel through filter 240 aided by the longitudinal electric fieldcreated by ion flow generator 250. The desiccant serves to furthercondition the sample gas before filtering for improved performance.

In still another embodiment shown in FIG. 15, spectrometer 333 includesion filter 240 with a plurality of RF electrodes 340, 342, 344 and 346connected to an electric controller 30 which applies the asymmetricperiodic voltage to create the filtering field. DC compensation may alsobe applied to these electrodes. The ion flow generator 250 includes asecond plurality of discrete electrodes 348, 350, 352 and 354 dispersedamong but insulated from the discrete RF electrodes of the ion filterand connected to controller 30, which establishes a gradient between theelectrodes to generate an ion propelling transport field 252 along theflow path toward the detector 270. The electrodes may be coated with aninsulating material 358, as well as being isolated from each other byadequate insulation.

In the embodiment of FIG. 15, all the RF electrodes may be independentlydriven or tied together while the longitudinal field producingelectrodes have a potential gradient dropped across them. In oneembodiment, the voltages applied to the electrodes can be alternated sothat first a voltage is applied to generate the transverse RF electricfield 242 and then a voltage is applied to other or same electrodes togenerate the longitudinal ion transport field 252.

In still another embodiment, spectrometer embodiment 359 shown in FIG.16 includes RF electrodes 360, 362, which provide the asymmetric ionfiltering electric field 252 are disposed on the outside walls ofinsulative substrates 52, 54. Resistive layers 370 and 372 may be aresistive ceramic material deposited on the inside walls of insulatingsubstrates 52 and 54, respectively. Terminal electrodes 374-375, and377-378 make contact with each resistive layer is shown to enable avoltage drop across each resistive layer to generate the ion propellinglongitudinal electric field 252. Thus, electrodes 374 and 377 may eachbe at −100 volts while electrodes 375 and 378 are at −1000 volts, forexample.

In the embodiment of FIG. 17, spectrometer 379 has discrete electrodes380-386 on substrate 52 and 387-394 on substrate 54 which cooperate toproduce an electrical field or fields. The net effect provides bothtransverse and longitudinal field components to both filter and propelthe ions. A traveling wave voltage of the formVcos (wt−kz)where k=2π/λ is the wave number has an associated electric field withboth transverse and longitudinal components 242+252. For a planarsystem, each succeeding set of opposing electrodes is excited by avoltage source at a fixed phase difference from the voltage sourceapplied to the adjacent set of opposing electrodes.

Thus, electrodes 380 and 387 are excited with a voltage of vcos(wt)while electrodes 381 and 388 are excited with a voltage of vcos (wt+120)and so on as shown in FIG. 17. Traveling wave voltages requiremultiphase voltage excitations, the simplest being a two phaseexcitation. So, a two conductor ribbon could also be wound around a ductdefining the gap with one conductor excited at vcos (wt) and the otherconductor excited at vsin (wt). Three phase excitations could beincorporated if the conductor ribbon or tape had three conductors.

In an alternative of the embodiment of FIG. 17, the discrete electrodes380-386 and 387-394 are still driven to produce both transverse andlongitudinal fields to both filter and propel the ions. The PFAIMS RFsignal is applied to the electrodes to generate the transverse RF field,which may involve one electrode on each substrate or multipleelectrodes. Compensation is also generated, either by varying the dutycycle or the like of the RF, or by applying a DC bias to the electrodes,which may involve one electrode on each substrate or multipleelectrodes. Finally, the ion flow generator includes a selection ofthese electrodes biased to different voltage levels (e.g., 1000 vdc onelectrodes 380 and 387 and 100 vdc on electrodes 386 and 393) togenerate a gradient along the flow path. Compensation voltage applied tothe RF filter field opens the filter to passage of a desired ion speciesif present in the sample as propelled by the flow generator. If thecompensation voltage is scanned, then a complete spectrum of thecompounds in a sample can be gathered.

In a further embodiment of the invention, ion filtering is achievedwithout the need for compensation of the filter field. As shown in FIG.18, in one illustrative embodiment, spectrometer 410 has a single RF(high frequency, high voltage) filter electrode 412 on substrate 52. Asegmented filter-detector electrode set 414 on substrate 54 has aplurality of electrodes 414 a-414 n. Electrode 412 faces set 414 overflow path 26. Strips 414 a-414 n are maintained at virtual ground, whilethe asymmetric field signal is applied to the filter electrode 412.

It will be further appreciated that, referring to FIG. 2, ions 19 flowin the alternating asymmetric electric field 25 and travel inoscillating paths that are vectored toward collision with a filterelectrode, and collision will occur in absence of adequate compensation.In the embodiment of FIG. 18, the absence of compensation favorablyenables driving of the ions to various electrodes of the segmentedelectrode set 414. Thus all of the ions are allowed to reach and contactone of the electrodes 414 a-414 n. These ions thus deposit their chargesupon such contact, which is monitored such as with current meters 421,421. (It will be further appreciated that this arrangement isillustrative and not limiting. For example, the filter electrode may besegmented, similar to the filter-detector electrode set, where ions alsowill be detected thereon.)

In an illustrative embodiment, upstream biasing effects which ions flowto the filter. For example, a sample S flows (“IN”) into an ionizationregion 415 subject to ionization source 416. Electrodes 417, 418, 419are biased to deflect and effect flow of the resulting ions. Positivebias on electrode 419 repels positive ions toward the filter andelectrodes 417, 418 being negatively biased attract the positive ionsinto the central flow of filter 420, while negative ions are neutralizedon electrode 419 and which are then swept out (“OUT”) of the region.Negative bias on electrode 419 repels negative ions toward the filterand electrodes 417, 418 being positively biased attract the negativeions into the central flow path 26 of filter 420, while positive ionsare neutralized on electrode 419.

The path taken by a particular ion in the filter is mostly a function ofion size, cross-section and charge, which will determine which of theelectrodes 414 a-414 n a particular species will drive into. Thisspecies identification also reflects the polarity of the ions and thehigh/low field mobility differences (“alpha”) of those ions. Thus aparticular ion species can be identified based on its trajectory (i.e.,which electrode is hit) and knowledge of the signals applied, the fieldsgenerated, and the transport characteristics (such as whether gas orelectric field).

In practice of the filter function, where the upstream biasing admitspositive ions 19+ into the filter, those positive ions with an alphaless than zero will have a mobility decrease with an increase of thepositively offset applied RF field (waveform 25 a). This will effect thetrajectory of these ions toward downstream detector electrode 414 n.However, a positive ion 19+ with an alpha greater than zero will have amobility increase with an increase of the negatively offset applied RFfield (waveform 25 b), which in turn will shorten the ion trajectorytoward the nearer detector electrodes.

Similarly, where the filter is biased to admit negative ions, a negativeion 19− with an alpha less than zero will have a mobility increase withan increase of the positively offset applied RF field waveform 25 a;this will tend to effect the ion trajectory toward downstream detectorelectrode 414 n. However, a negative ion 19− with an alpha greater thanzero will have a mobility increase with an increase of the negativelyoffset applied RF field waveform 25 b, which in turn will tend toshorten the ion trajectory toward the nearer detector electrodes. Thus,ions can be both filtered and detected in spectrometer 410 without theneed for compensation.

Various embodiments of the present invention are able to identifycompounds in a chemical sample down to trace amounts. In FIG. 19,identification of individual constituents of a mixture is demonstratedby the distinct and separate Benzene peaks 422 and acetone peaks 424obtained in practice of the invention. Three plots are superimposed inFIG. 19. The first plot is for benzene and acetone (1-3) ppm; the secondplot is for benzene and acetone (trace). The bottom plot shows benzenealone. It therefore can be observed that the acetone peak can be easilydistinguished from the benzene peak in practice of the presentinvention. This capability enables separation and identification of awide array of compounds in chemical samples in a compact andcost-effective method and apparatus of the invention.

Multiple use of electrodes is not limited to the examples set forthabove. Embodiments of the present invention lend themselves to the useof an electrospray ionization source nozzle because certain of theelectrodes can function both as the source for the PFAIMS andlongitudinal electrical field which transports the ions toward thedetector electrodes, but also as the electrospray electrodes whichcreate a fine spray sample for ionization. Thus, in accordance with thepresent invention, pumps 216 and 212, FIG. 9 of the prior art are eithereliminated or at least reduced in size and have lower flow rate andpower requirements.

In practice of the invention, by the incorporation of an ion flowgenerator which creates a longitudinal electric field in the directionof the intended ion travel, the ions are propelled through thetransversely directed compensated asymmetric electric field and onwardfor detection. The apparatus may include a detector or may deliver ionsto a detector.

In practice of the invention, pump and gas flow requirements aresimplified. By eliminating the high flow rate of pumps used in prior artspectrometers, a significant reduction in power consumption, size, andcost can be realized leading to a miniaturized spectrometer on a chip inpractice of embodiments of the invention.

Another benefit in practice of alternative embodiments of the inventionis that a flow of clean filtered air can be applied in a directionopposite the direction of the motion of the ions. In this way, anyneutrals in the sample gas which were not ionized are deflected away anddo not enter the ion analysis region. The result is the reduction orelimination of ion clustering, and reduction of the impact of humidityon sensor performance. Because the flow rates are low, it is possible toincorporate integrated micromachined components. Molecular sieves can belocated close to the filter in order to absorb any neutral molecules inthe analysis region to reduce or prevent clustering.

Embodiments of the present invention employ a field asymmetric ionmobility filtering technique that uses compensated high frequency highvoltage waveforms and longitudinal e-field propulsion. The RF fields areapplied perpendicular to ion transport, with a planar configuration, butcoaxial, concentric, cylindrical and radial embodiments are also withinthe scope of the invention.

The spectrometer can be made extremely small, if required, and used inchemical and military applications, as a filter for a mass spectrometer,as a detector for a gas chromatograph, as a front end to a time offlight ion mobility spectrometer for increased resolution or as a filterfor a flexural plate wave device.

The present invention provides improved chemical analysis. The presentinvention overcomes cost, size or performance limitations of MS,TOF-IMS, FAIMS, and other prior art devices, in novel method andapparatus for chemical species discrimination based on ion mobility in acompact, fieldable packaging. These devices have the further ability torender simultaneous detection of a broad range of species, and have thecapability of simultaneous detection of both positive and negative ionsin a gas sample. Still further surprising is that this can be achievedin a cost-effective, compact, volume-manufacturable package that canoperate in the field with low power requirements and yet it is able togenerate definitive data that can fully identify various detectedspecies.

The present invention may be implemented using conventional or advancedmanufacturing techniques, such as MEMS or micromachining. Thesetechniques may include, for example, etching of smooth channels,chambers, dams, and intersections, and ports, forming and building uponsubstrates, etching and bonding, including anodic bonding and fusion,thin film processing and metallization applications, quartz machining,reactive ion etching, high temperature fusion bonding, photolithography,wet etching and the like.

Examples of applications for the present invention include chemicalsensors and explosives sensors, and the like. Various modifications ofthe specific embodiments set forth above are also within the spirit andscope of the invention. For example, it will be further appreciated thatembodiments of the invention may be practiced with coaxial, concentric,ring, cylindrical, radial or other features. For example, the electrodesof FIG. 17 may be ring electrodes; as well, structural variations mayappear in combination, such as where the electrodes of FIG. 11 are ringelectrodes and the remaining layers and electrodes are coaxial andcylindrical, for example.

The examples disclosed herein are shown by way of illustration and notby way of limitation. Although specific features of the invention areshown in some drawings and not in others, this is for convenience onlyas various features may be combined with any or all of the otherfeatures in accordance with the invention.

1. An ion mobility analyzer, comprising: an ion source, a chip assemblycoupled to receive a flow of ions from the ion source, and having aspaced filter including a first substrate with a first filter electrodeconnected to the substrate, a second filter electrode spaced away fromthe first filter electrode to thereby define an analytical gap betweenthe first and second filter electrodes and a portion of a flow paththrough which the ion flow occurs, and a controller connected to atleast one of the first and second filter electrodes to generate a timevarying electric field between the first and second filter electrodesand having a field characteristic for separating ion species while theion species are flowing through the analytical gap.
 2. The Analyzer ofclaim 1, wherein the time varying electric field drives a portion of theion species onto a surface along the flow path where the portion of ionspecies are neutralized into neutrals.
 3. The Analyzer of claim 1,comprising an ion flow generator for generating a field within theanalytical gap for enabling transportation of ions within the analyticalgap.
 4. The Analyzer of claim 1, comprising a clean gas inlet that isconfigured for introducing clean gas flow into the chip assembly.
 5. TheAnalyzer of claim 4, wherein the clean gas includes at least one ofdehumidified air and filtered air.
 6. The Analyzer of claim 1,comprising a front end for delivering a sample to the ion source.
 7. TheAnalyzer of claim 6, wherein the front end includes at least one of agas chromatograph and a liquid chromatograph.
 8. The Analyzer of claim2, comprising a flow of gas in a direction opposite the direction oftransportation of ions within the analytical gap to remove at least aportion of the neutrals from the filter.
 9. The Analyzer of claim 1,comprising a flow of gas out of the filter to cleanse the filter of atleast a portion of neutrals.
 10. The Analyzer of claim 1, wherein thefilter has a micromachined surface.
 11. The Analyzer of claim 1,comprising a spacer for spacing apart the first and second filterelectrodes.
 12. The Analyzer of claim 3, comprising a sidewall defininga spacer for spacing apart first and second ion flow generatingelectrodes of the ion flow generator.
 13. The Analyzer of claim 12,wherein the at least one of the filter electrodes and one of the flowgenerating electrodes are the same electrode.
 14. The Analyzer of claim1, comprising a second substrate coupled to the second electrode anddisposed in juxtaposition to the first substrate.
 15. The Analyzer ofclaim 14, the first substrate and the second substrate being bonded. 16.The Analyzer of claim 1, wherein the controller includes a substratehaving a voltage generator circuit formed thereon.
 17. The Analyzer ofclaim 1, wherein the controller includes a substrate having anamplifier.
 18. The Analyzer of claim 1, wherein the controller includesa substrate bonded to the chip assembly.
 19. The Analyzer of claim 1,wherein the controller is included in the chip assembly.
 20. TheAnalyzer of claim 1, wherein the controller is formed on the substrate.21. The Analyzer of claim 1, wherein at least one of the first andsecond filter electrodes includes an electrode deposited on thesubstrate.
 22. The Analyzer of claim 21, wherein the electrode includesmetal.
 23. The Analyzer of claim 1, wherein the substrate includes achannel for defining the flow path including the ion flow.
 24. TheAnalyzer of claim 23, wherein the channel is formed by lithography. 25.The Analyzer of claim 23, wherein the channel or an electrode is formedby a process selected from at least one of micromachining, etching, wetetching, and reactive ion etching, bonding, depositing, metallization,fusion, and building upon.
 26. The Analyzer of claim 1, wherein the ionflow substantially continuously carries a portion of the ions throughthe analytical gap over a period of time.
 27. The Analyzer of claim 1comprising a carrier gas flowing within the flow path.
 28. The Analyzerof claim 1, wherein the controller generates a time varying electricfield for controlling a range of motion of an ion continuously flowingthrough the analytical gap.
 29. The Analyzer of claim 1, wherein thechip assembly includes at least one detector for detecting ions of atleast a portion of the sample.
 30. The Analyzer of claim 1, wherein thecontroller includes an time varying voltage generator for generating thetime varying electric field over a range of magnitudes and range offrequencies.
 31. The Analyzer of claim 1, wherein the controllerincludes a compensation voltage generator for generating a compensationfield to pass selected ions through the analytical gap.
 32. The Analyzerof claim 31, wherein the controller controls the magnitude of thecompensation voltage to control the magnitude of the compensation field.33. The Analyzer of claim 1, wherein the controller includes amicroprocessor for selectively controlling at least one of the timevarying electric field and a compensation field.
 34. The Analyzer ofclaim 24, wherein the channel for defining the flow path issubstantially adjacent to a silicon substrate.
 35. The Analyzer of claim1, wherein the chip assembly includes a plurality of layers, a firstlayer including the filter, and a second layer including the controller.36. The Analyzer of claim 11, wherein at least a portion of the spacerextends along the spaced filter.
 37. The Analyzer of claim 11, whereinthe spacer comprises at least one of glass, ceramic, silicon, and pyrex.38. The Analyzer of claim 11, wherein the spacer includes insulatingmaterial.
 39. The Analyzer of claim 1, wherein the chip assemblyincludes a resistive layer for controlling the flow of ions.
 40. TheAnalyzer of claim 39, wherein the resistive layer includes depositedresistive materials.
 41. The Analyzer of claim 1 comprising a heater forheating a portion of the ion flow passing through the analytical gap.42. The Analyzer of claim 1, wherein a plurality of chips are bondedtogether to form the Analyzer.
 43. The Analyzer of claim 1, wherein thechip assembly includes at least one of a desiccant, a gas conditioner, apump, the ion source, an amplifier, a molecular sieve, a dopant inlet,and an insulating medium.
 44. The Analyzer of claim 1, wherein the chipassembly couples to at least one of an MS, IMS, DMS, and a mobilitybased analyzer.
 45. The Analyzer of claim 1, wherein the analyzeroperates as a pre-filter for one of an MS, IMS, DMS, and a mobilitybased analyzer.
 46. The Analyzer of claim 1, comprising a plurality ofion flows, each ion flow associated with a time varying field forfiltering a portion of ions.
 47. The Analyzer of claim 1, wherein theion source includes an electrospray ion source.
 48. An ion mobilitybased analyzer comprising: a first pair of opposing electrodes forgenerating a time varying electric field therebetween, a second pair ofopposing electrodes, the second pair of electrodes being biased inrelation to the first pair of electrodes to generate an ion flow along aflow path including the first and second pair of electrodes.
 49. TheAnalyzer of claim 48, wherein the second pair of opposing electrodesincludes a time varying field therebetween.
 50. The Analyzer of claim48, wherein the time varying electric field is substantially traverse tothe ion flow.
 51. A method for manufacturing an ion mobility basedanalyzer comprising: providing a substrate, lithographically defining anion filter region having first and second electrodes for generating atime varying electric field therebetween, providing a controller tocontrol the time varying electric field.
 52. A method for manufacturingan ion mobility based analyzer comprising: providing a substrate,micromachining the substrate to define an ion filter region having firstand second electrodes for generating a time varying electric fieldtherebetween, providing a controller to control the time varyingelectric field.